1. Field of the Invention
The present invention relates to an image pickup device and a defect detecting method, and particularly to an image pickup device and a defect detecting method that enable defect detection in a solid-state image pickup element of an image pickup device without a light shielding device for blocking light such as an iris or the like to be made with more ease and at low cost.
2. Description of the Related Art
Correction of a defective pixel occurring in a solid-state image pickup element includes static defect correction and dynamic defect correction.
Static defect correction corrects a defective pixel detected by testing a solid-state image pickup element before shipment from a factory or the like. In static defect correction, the addresses of all defective pixels are stored in a nonvolatile memory as a result of the test. It therefore suffices to interpolate pixel values for the pixels corresponding to the addresses on the basis of normal peripheral pixels. The defective pixels can thus be corrected easily.
However, because of the need to test the solid-state image pickup element in advance and provide a nonvolatile memory, an increase in chip cost is inevitable. In addition, when a defect in a defective pixel changes in degree depending on states such as temperature, a voltage value and the like, the degree of the defect at the time of the test and the degree of the defect at the time of the defect correction may differ from each other, so that the defective pixel may not be corrected properly.
On the other hand, dynamic defect correction detects a defective pixel by for example performing relative comparison between the pixel values of a pixel as a detection object and peripheral pixels during streaming, and corrects the detected defective pixel. In dynamic defect correction, defective pixels are detected at any time. Thus, it is not necessary to provide a nonvolatile memory for storing the addresses of all defective pixels, and it suffices to provide a small-capacity line memory.
A method for detecting such defective pixels differs according to the algorithm of a signal processing circuit that performs the method, and the accuracy of detection and correction of defective pixels is greatly affected by the processing power of the signal processing circuit.
For example, recently, solid-state image pickup elements have been miniaturized and increased in the number of pixels, and the light receiving area of photodiodes (PDs) forming pixels has been decreased steadily. In order to remedy this, there is a tendency to increase the light receiving area of PDs even if only slightly by making an amplifying transistor, a reset transistor, a floating diffusion (FD) and the like shared by a plurality of pixels. Accordingly, when a defect occurs in an FD shared by a plurality of pixels, for example, all the sharing pixels appear to be defective pixels. Therefore dynamic defect detection requires more accurate defect detection. In addition, the larger the number of sharing pixels, the higher the required capacity of a line memory used to detect defective pixels.
Incidentally, a technique is proposed which detects a defective pixel by performing image pickup in an image pickup device in a state of an iris being closed once, that is, in a state of a solid-state image pickup element being shielded from light when power is turned on, for example, and detecting a pixel value that stands out from the pixel values of respective pixels of the solid-state image pickup element.
For example, there is a technique for detecting and correcting defective pixels having different temperature characteristics by performing image pickup in a state of an iris being closed (see Japanese Patent Laid-Open No. 2009-105582, hereinafter referred to as Patent Document 1).